This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-189734 filed on Jun. 20, 2000.
1. Field of the Invention
The present invention relates to an air-fuel ratio controller or an internal combustion engine, which controller controls the amount of fuel injection.
2. Description of Related Art
In recent automobiles, a three-way catalytic converter is located in the exhaust pipe for the cleaning of exhaust gas, and an air-fuel ratio sensor also is located on the upstream side of the catalytic converter to determine the amount of fuel injection based on state feedback for bringing the air-fuel ratio of the exhaust gas close to a purification window (around theoretical ideal air-fuel ratio) in response to output of the air-fuel ratio sensor, so that exhaust gas is cleaned efficiently. The air-fuel ratio control is generally based on a model system of the controlled object ranging from the fuel injection valve down to the air-fuel ratio sensor to calculate feedback gain of the system with an optimizing regulator, to calculate an air-fuel ratio correction factor by using the calculated feedback again, and to correct a base fuel injection amount, which has been determined from the operational states of the engine, in response to the calculated air-fuel ratio correction factor, etc., thereby determining the amount of fuel injection, as described in JP-A-7-11995.
The above-described conventional air-fuel ratio control repeats the calculation of feedback gain with the optimizing regulator by varying the weighting parameters Q and R of the criterion function J so that the value of J is minimum at which the optimal control characteristics are obtained. Thus, it is necessary to calculate values of feedback gain in advance to cope with the difficulty of calculating the feedback gain by an on-line real-time process. On this account, it cannot vary the feedback gain continuously in accordance with the operational states of the engine, but has to control the fuel injection at a smaller feedback gain for the sake of control stability, thereby resulting unfavorably in a degraded accuracy of air-fuel ratio control.
An object of the present invention is to provide an air-fuel ratio controller for internal combustion engines which is capable of calculating the control parameters of air-fuel ratio control by an on-line real-time process, thereby varying control parameters continuously in response to operational states of the engine and thus improving control accuracy of air-fuel ratio.
According to the present invention, an inventive air-fuel ratio controller is designed to calculate coefficients of a characteristic polynomial of a control model which simulates the controlled object ranging from the fuel injection valve down to the air-fuel ratio detecting means based on a pole arrangement scheme which makes roots, which are equal in number to the dead time of the control model or equal in number to nxe2x88x921 or nxe2x88x922 (where n is the degree of the characteristic polynomial), to be zero, calculate control parameters based on coefficients of the characteristic polynomial of the control model and model parameters with a control parameter calculating means, and calculate from the control parameters an air-fuel ratio correction factor with an air-fuel ratio correction factor calculation means.
Calculating coefficients of the characteristic polynomial of the control model based on a pole arrangement scheme which makes roots, which are equal in number to the dead time of the control model or equal in number to nxe2x88x921 or nxe2x88x922 to be zero, enables calculation of coefficients of the characteristic polynomial and revision of control parameters by an on-line real-time process. In consequence, it becomes possible to vary control parameters continuously in response to operational states of the engine, thereby improving control accuracy of the air-fuel ratio.